Page 649 - Mechanical Engineers' Handbook (Volume 2)

640 Controller Design

Figure 18 Effects of second-order lead compensation on a poorly damped system (electronic integra-
tion): (a) root locus; (b) closed-loop frequency response.

substantial improvement in loop gain for low but is of little use for 0.3. For
2
2
2
0.10, lag compensation allows K u2 to be increased from 0.10 to 0.27 s 1 with comparable
levels of stability (gain margin 6 dB). It should be noted that very little advantage is provided
by the use of a higher order low-pass filter instead of the first-order type.
In summary, the use of lead compensation to improve the damping of a poorly damped
system is not straightforward, and the end result may be a marginal improvement in closed-
loop performance. Lag compensation is more straightforward but offers only a modest im-
provement in performance. If substantial improvement in system damping and performance